Van type vehicles for passengers and for cargo are frequently equipped with sliding side doors. Rollers support and guide such sliding doors by running in fixed tracks. Sliding doors may be positioned on both sides of a vehicle or a single sliding door may be positioned on one side of the vehicle. However, most vans include a single sliding door positioned on the side of the van opposite the vehicle operator's station. When seated at the vehicle operator's station, a vehicle operator can open or close sliding doors of this type only by leaving the operator's station and either walking around the outside of the vehicle to the sliding door or crossing inside the vehicle to the sliding door. Crossing inside the vehicle is often difficult or impossible due to the presence of cargo and/or passengers positioned inside the van between the operator's station and the door. If a sliding door is positioned on the same side of the van as the operator's station, the operator still must leave the operator's station to open and shut the sliding door from either the inside or outside of the vehicle.
To allow an operator to open and close a sliding door from the operator's station and/or another location remote from the sliding door, power operated sliding door closure systems have been developed. An example of such a system is disclosed in U.S. Pat. No. 5,396,158 which issued Mar. 7, 1995 to Joseph D. Long et al. The Long et al. patent discloses a sliding door closure apparatus that includes a sliding door mounted in a van on rollers and slidably supported in upper, center and lower tracks. An opening and closing module is mounted inside the van adjacent the center track. A front cable is attached to a front cable drive pulley or drum and extends from the front drum to the sliding door through a front cable roller guide assembly. A rear cable is attached to a rear cable drive pulley or drum and extends from the rear drum to the sliding door through a rear cable roller guide assembly. The front and rear cable drive drums each have a large diameter helical cable groove.
A motor drive unit rotates the front and rear cable drive drums to move the sliding door. The motor drive unit, as best shown in FIG. 3 of the '158 patent, comprises an electric motor that drives a drive gear that is coaxially aligned with the front and rear cable drive drums. A lost motion connection is provided between the drive gear and the front cable drive drum in the form of a drive lug that is carried by the drive gear and a complementary drive lug that is carried by the front cable drive drum. A lost motion connection is also provided between the drive gear and the rear cable drive drum in the form of a second drive lug that is carried by the drive spool and a second complementary lug that is carried by the rear cable drive drum. As seen in FIGS. 2 and 3 of the '158 patent, a coil spring is seated in an annular opening in the cable drive drums. An upper spring end is anchored on the rear cable drive drum and a lower spring end is anchored on the front cable drive drum. The coil spring is a tension retaining spring that urges the front cable drive drum in the counterclockwise winding direction and the rear cable drive spool in the opposite clockwise winding direction so that the front and rear cables are maintained in tension at all times.